Gaseous dielectric materials

ABSTRACT

Materials are described which are useful as gaseous dielectric insulators in electrical devices. These materials are a group of sulfur compounds which have two fluorine atoms and at least one perfluoroalkylimino group attached to the sulfur atom. It has been discovered that the substitution of a perfluoroalkylimino group for an oxygen atom attached to a sulfur atom increases the dielectric breakdown voltage of the molecule. These gaseous materials can be used both in substantially pure form or mixed with inert gaseous material. They exhibit high breakdown voltages and in addition do not yield undesirable reaction products when exposed to dielectric breakdown.

United States Patent Griffiths July 4, 1972 54] GASEOUS DIELECTRICMATERIALS 2,221,671 11/1940 Cooper ..252 66 [72] inventor: James EdwardGnfflths, Murray Hill, NJ. Primary Examineramfred L Leavm [73] Assignee:Bell Telephone Laboratories, Incorporated, ssis xami r-lanyce A- B llMurray Hill, NJ. Att0rneyR. J. Guenther and Edwin B. Cave [21] Appl'102,706 Materials are described which are useful as gaseous dielectricinsulators in electrical devices. These materials are a group of 521 US.(:1 ..252/63.7, 174/15 200/149 Sulfur comPounds which have two Wineatoms and at least 252/66 310/55 333/95 336/94 one perfluoroalkyliminogroup attached to the sulfur atom. 1t 5 1 1111. c1. .116, 3/18 has beendiswvered that substiwfim Perfluma'" 581 Field 6: Search ..252/63.7 66-174/1s' 336/94- kylimin" 3mm attached a 8mm 317/244. 333/95 increasesthe dielectric breakdown voltage of the molecule. These gaseousmaterials can be used both in substantially pure form or mixed withinert gaseous material. They exhibit high [56] References cued breakdownvoltages and in addition do not yield undesirable UNITED ES PATENTSreaction products when exposed to dielectric breakdown.

2,21 1,019 8/l 940 Lommel 252/63.7 9 Claims, 5 Drawing Figures VAPORPHASE BREAKDOWN VOLTAGE (vows) llllll p (TO-RR) x DISTANCE (1111.5)

P'ATENTEUJU '4 m2 3. 6 74.6 96

sum 1 or 2 Dul FIG. 2

x X \\XLE5 I ELECTRIC CONDENSER 2O ELECTRIC TRANSIFORMER 5 E //v VEN r09J. E. GRIFFITHS AT RNEY P'A'TENTEDJUL 4 I972 SHEET 2 OF 2 FIG. 4

5 2 E m U G W A W FIG. 5

VAPOR PHASE p (TORR) x DISTANCE (MILS) 1 cxsrzous DIELECTRIC MATERIALSBACKGROUND or THE INVEN 'I ION l. Field of the Invention The inventionrelates to gaseous dielectric materials and electrical devices whichmake use of these gaseous dielectric materials.

. 2. Description of the Prior Art Many electrical devices use separationof conductors to achieve electrical insulation. In these devicesatmospheric air is used as the dielectric insulator to preventconduction between these separated electrical conductors. For manycases, especially where large voltage gradients are not involved,atmospheric air serves perfectly well as the dielectric insulatingmaterial.

ln electrical devices where large voltage gradients are resent,dielectric breakdown is often a problem. Further separation of theconductors or the use of solid dielectric insulation is often precludedby other considerations, such as device design and heat dissipationproblemsJn these cases the use of gaseous materials with substantiallyhigher dielectric breakdown voltages than air is often advantageous.Examples of electrical devices which might require the use of gaseousdielectric materials are electric generators, electric transformers,electrical switching apparatus, cables, and waveguides.

The importance of high breakdown voltages in gaseous dielectrics isparticularly well illustrated in the case of waveguides used in radartransmitters. Here, the range of the radar apparatus depends strongly onthe power of the transmitted radar signal. This power is often limitedby dielectric breakdown in waveguides used to feed the radar antenna.Indeed, the power is proportional to the square of the electric fieldsset up in the waveguide. Thus doubling the electric field increases themaximum power which can be supported by the waveguide without dielectricbreakdown by a factor of 4. For this reason, the use of a gaseousmaterial with dielectric breakdown voltages considerably larger than nowavailable would greatly increase the range and usefulness of presentlyavailable radar equipment without substantial change in presentlyavailable equipment of great economic penalty.

Similar conditions can I be applied to other electrical Selection of thedielectric gases is based on the discovery that the substitution ofperfluoroalkylimino groups for an oxygen group in a sulfur 'oxyfluoridecompound increases the dielecdevices, especially where miniaturizationand space con-.;

siderationsare of importance.

Typical substances which have been used inthe past as gaseousdielectrics have been SF and 50,. These substances have limiteddielectric breakdown voltages and in addition often yield undesirablebreakdown products when dielectric SUMMARY OF THE INVENTION Theinvention is electrical devices inwhich certain gaseous materials areused as dielectric insulators in either substan tially pure form'or incombination other inert gases.

,S=NC F:

tric breakdown voltage. Specifically the substitution of aperfluoroalkylimino group for the oxygen group in SOF yields a compoundwith the general formula SN(R)F, which has superior dielectricproperties such as higher breakdown voltage. The perfluoroalkyl groupdesignated by .R in the general formulas given in this application mayhave up tothree carbon atoms. Greater, than three carbon atoms in theperfluoroalkyl group will yield compounds which do not remain gaseousunder conditions in which electrical devices operate. For example, thebreakdown voltage of SN(CF,)F, was shown to be significantly greaterthan SOF,. In addition, the compound sulfuryl fluoride SO,F, has beenfound to exhibit the desirable dielectric properties. The substitutionof a perfluoroalkylimino group for either one or both of the oxygens inSO,F, also yields compounds with desirable dielectric. properties. Thesecompounds are SN(R)OF, and S(RN),F,. Examples of a compound from eachgroup aretrifluoromethylimino thionyl fluoride, SN(CF,)OF, andbis-(trifluoromethylimino) sulfur difluoride S(NCF,),F, andcorresponding ethyl and propyl derivatives. While the invention isdescribed in terms of substituting a perfluoroalkylimino group for anoxygen group in a sulfur oxyfluoro compound, it is understood that anyconvenient method of preparation may be to prepare the inventivecompound.

There are a large variety of electrical devices in which thesedielectric gases could be used. These include condensers, generators,transformers, electric cable, switching apparatus and waveguides, toname a few. 1

It should be understood that these dielectric gases can either be usedin substantially pure fonn or mixed with other inert gases. For example,in devices where only a modest improvement in breakdown voltage isrequired, small amounts of the inventive dielectric gases might be mixedwith air. Typically 10-100 percent by volume of the dielectric gas isused. Also, other additional inert gases are used either because oftheir improved dielectric characteristics or for more efficient coolingof the electrical apparatus. Such gues are nitrogen, helium, carbondioxide and hydrogen, to name a few.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side view of an electricgenerator with entrance and exit tubes for introducing and. removing thedielectric gaseous material; 7

FIG. 2 is a side view of an electric transformer showing en trance andexit tubes for dielectric gaseous material;

FIG. 3 is a side view of an electric capacitor with entrance I and exittubes for the dielectric gaseous material;

FIG. 4 is a side view of a waveguide with entrance and exit tubes fordielectric gaseous material; and

FIG. 5 is agraph showing data on the dielectric properties of severalgaseous substances on coordinates of dielectric breakdown voltage versuspressure in torr multiplied by electrode separation in mils.

DETAILED DESCRIPTION l Glossary of Compounds For convenient reference,some of the compounds referred to in the disclosure are given below. Thecompounds are identified by their structural formulas and molecularformulas SN (C Fg) Fr Pentafluoroethylimino sulfur difluoride.

compound was pyllmino sulfur dlfluorlde.

Pentafluoroethylimino heptafluoroisopro- 2. Breakdown VoltagesDielectric gaes are used primarily for insulating purposes in electricaldevices. Other possible uses are for cooling purposes -or to alter thedielectric response to a particular electrical signal. Breakdownvoltages are a convenient measurement of the effectiveness of dielectricgases used for insulating purposes. I

I The breakdown voltages were measured using an evacuable glass cellcontaining parallel-plate electrodes made of nickel. One electrode wasstationary and the other was movable so that electrode separation couldbe varied. Care was taken to maintain a uniform'field between theelectrodes. Thus the diameter of the electrodes was for all measurementsgreater than lO times the electrode separation. Also, the edges of theelectrodes-were rounded so as to eliminate any sharp in the electrodeconfiguration which might lead to non-uniform electric fields. Electrodeseparations varied in these experiments from about 80 niilsto aboutmils. The pressure was varied from approximately atmospheric pressuredown to approximately l0 torr. Over this range the voltage breakdown wasfound to approximate Paschen's Law in that the voltage breakdowndepended only on the product of gas pressure and electrode separation.Data on breakdown voltage was obtained bysettingthe electrodes at agiven separation, in-

standard for dielectric gases. The substitution of a perfluoroalkyliminogroup for either one or both of the oxygens in SO,F, also yieldscompounds with improved dielectric breakdown characteristics. Again thenumber of carbon atoms in the alkyl group should be less than four toinsure that the dielectric substance remains gaseous under typicaloperating conditions for the electrical devices. Typical compounds withone or both oxygem replaced by the imino group are trifluoromethyliminothionyl ditluoride and bis-( trifluorornethylimino) sulfur fluoride andcorresponding ethyl and propyl derivatives.

3. Electrical Devices FIG. 1 shows an electric generator 10 in whichprovision by way of inlet 1 l and outlet 12 tubes has been made tointroduce a dielectric gas. This can be done either by continuouslyallowing the dielectric gas to flow through the electric aptroducing thedielectric gas' into the gas cell at a pressure near atmosphericpressure and then slowly increasing the voltage on the electrodes untilbreakdown occurred. The pressure of the dielectric gas was thenreducedand the voltage again increased slowly to where breakdown occurred. 7

Since different dielectric gases can be substituted in the apparatuswithout changing electrode configuration, the above procedure yieldedquite'reliable data on-the relative breakdown voltages of the gasesmeasured.

In order to illustrate the advantage of substituting a perparatus, orby'sealing the gas in the electrical apparatus. The composition of thedielectric gas might involve just one gas with high breakdown voltage ora'mixture of such gas or gases with several inert gases.

FIG. 2 shows a transformer 15 also provided with means of introducing adielectric gas to improve electrical perforrnance. Inlet 16 and outlet17 tubes are used to introduce the gas. Again the dielectric gas mightbe continuously flowed through the electrical apparatus or sealed intothe electrical apparatus.

FIG. 3 shows an electrical condenser 20 in which provision in the formof inlet 21 and outlet 22 tubes is made to introduce I a dielectric gas.

fluoroimino group for an oxygen group in a sulfur compound,

dielectric breakdown data was taken on two compounds related to oneanother by this substitution. The sulfur-oxygen compound chosen wasthionyl fluoride, SOF,. The substituted trifluoromethylimino sulfurdifluoride, SMCFQF, The results of these measurements are given in FIG.5. It should be recognized that SOF, itself has quite high breakdownvoltages. In fact, it exceeds in breakdown voltage such well-knowndielectric materials as SF and S0,. As can be seen from FIG. 5. thesubstitution of a perfluoroalkylimino group for the oxygen groupattached to the sulfur atom improves the dielectric breakdowncharacteristics of the material. Theperfluoroalkyl group may have up tothree carbon atoms. Higher homologues may liquify under some of theoperating conditions of electrical devices.

The dielectric breakdown voltages of SO,F, were also found to be quitedesirable. For example, the breakdown voltage of this substance wasfound to be greater than SF an oftenused FIG. 4 is a portion of awaveguide 25 in which provision has been made to'introduce a dielectricgas. This provision is an inlet 26 and outlet 27 tube. Again thedielectric gas could be continuously flowed through the apparatus orsealed permanently into the apparatus.

Gaseous dielectric materials are also useful in other electrical devicesthan shown in FIGS. I through 4, such as electrical cable, electricalswitching devices, etc.

What is claimed is:

I. An electrical apparatus with means for biasing a first portionrelative to a second portion in which the interstices between said firstand second portions contain a dielectric gas characterized in that thedielectric gas comprises 10-100 percent by volume of a compound selectedfrom the group consisting of SN(R)F,,-SN(R)OF, and S(NR) F, in which theR represents a perfluoroalkyl group with up to three carbon atoms.

2. The electrical apparatus of claim 1 in which the interstices containfrom 0-90 percent of a gas selected from a group consisting of nitrogen,helium, air, carbon dioxide and hydrogen.

3. The electrical apparatus of claim 1 in which the first and secondportions are physically separated. 7

4. The apparatus of claim 3 in which the said first and second portionscomprise an electric generator.

6 5. The electrical apparatus of claim 3 in which said first and 8. Theelectrical apparatus of claim 1 in which the first and second portionscomprise an electric transformer. second portions are in DC electricalcontact.

6. The electrical apparatus of claim 3 in which the said first 9. Theelectrical apparatus of claim 8 in which the said first and secondportions comprise an electric condenser. and second portions comprise awaveguide.

7. The electrical apparatus of claim 3 in which the said first 5 andsecond portions compnse an electrical switch. H

2. The electrical apparatus of claim 1 in which the interstices containfrom 0-90 percent of a gas selected from a group consisting of nitrogen,helium, air, carbon dioxide and hydrogen.
 3. The electrical apparatus ofclaim 1 in which the first and second portions are physically separated.4. The apparatus of claim 3 in which the said first and second portionscomprise an electric generator.
 5. The electrical apparatus of claim 3in which said first and second portions comprise an electrictransformer.
 6. The electrical apparatus of claim 3 in which the saidfirst and second portions comprise an electric condenser.
 7. Theelectrical apparatus of claim 3 in which the said first and secondportions comprise an electrical switch.
 8. The electrical apparatus ofclaim 1 in which the first and second portions are in D.C. electricalcontact.
 9. The electrical apparatus of claim 8 in which the said firstand second portions comprise a waveguide.